1. Field of the Invention
In general, an industrial automation system comprises a multiplicity of automation devices that are networked to one another by an industrial communication network and is used within the context of production or process automation to control or regulate installations, machines or devices. On account of time-critical constraints in technical systems that are automated via industrial automation systems, real time communication protocols, such as Profinet, Profibus or Real-Time-Ethernet, are predominantly used in industrial communication networks for communication between automation devices.
2. Description of the Related Art
Interruptions in communication links between computer units in an industrial automation system or automation devices can result in undesirable or unnecessary repetition of transmission of a service request. This causes additional utilization of communication links in the industrial automation system, which can result in further system disturbances or errors. Furthermore, messages that are not transmitted or that are not transmitted completely can prevent an industrial automation system from changing to or remaining in a safe operating state, for example. This can finally result in failure of a complete production installation and costly production stoppage. A particular set of problems arises in industrial automation systems regularly as a result of report traffic with comparatively many but relatively short messages, as a result of which the above problems are amplified.
EP 2 343 857 A1 describes a network node for a communication network that comprises a first network portion and a second network portion connected to the latter. Whereas a spanning tree protocol is used in the first network portion, a second protocol that differs from the protocol of the first network portion is used in the second network portion. The network node is set up as an element for the second network portion and is designed for communication within the second network portion. Furthermore, the network node is designed and set up, via a spanning tree functionality, as a spanning tree main node for monitoring and controlling the second network portion. Hence, the second network portion can be treated as a virtual network node by the spanning tree protocol used in the first network portion by virtue of the network node undertaking a spanning tree protocol application as a spanning tree main node for other network nodes of the second network portion.
WO 2010/105828 A1 discloses a method for operating a communication network with redundancy properties that has a ring network topology. Within the communication network, communication devices are connected to one another by means of their data ports via data lines and interchange control data and useful data via the data lines based on communication protocols. In order to avoid continuous circling of messages in meshes of the communication network, the communication protocols are used to prevent transmission of messages via selected data ports on individual communication devices with the exception of messages for controlling and monitoring media redundancy. Within the communication network, two different communication protocols are applied in parallel with one another in the communication devices. By way of example, parallel application of the different communication protocols is achieved by assigning control over data ports that are to be blocked to a single communication protocol. Alternatively, parameters can be chosen for the communication protocols such that a first communication protocol does not block connections that are deemed active on the basis of a second communication protocol.
DE 10 2009 048 046 A1 discloses a method for connecting a network segment with a linear topology to a network portion with a ring topology, in which the network portion with the ring topology has a redundancy manager provided for it that monitors this network portion particularly for interruptions. The network segment with the linear topology has no redundancy manager provided for it, but rather two segment controllers at ends of the linear topology that control a connection to the network portion with the ring topology send control packets into the network segment with the linear topology. In this case, a first segment controller caters for data traffic linkage of the network segment with the linear topology to the network portion with the ring topology, while the second segment controller keeps its port that is provided for data traffic linkage to the network portion with the ring topology in a blocked state and receives only the control packets for the first segment controller. If the second segment controller recognizes an interruption in the network segment with the linear topology based on an absence of the control packets on the first segment controller, it switches its port that is provided for data traffic linkage to the network portion with the ring topology to a forwarding state. One disadvantage is that network nodes within the network segment with the linear topology cannot, following an interruption in a connection, independently reactivate their port that is associated with the interrupted connection, but rather have to wait for an instruction to do so from a segment controller. This slows down network reconfiguration following a connection failure.
U.S. Pat. No. 8,184,527 B2 also describes a method for network linkage of a ring portion to a closed ring in which a first and a second switch are provided for coupling the ring portion to the ring. In this case, a port of the first or second switch that is provided for data traffic linkage of the ring portion to the ring is blocked while a corresponding port of the respective other switch is activated. Here, the switch with the activated port sends data packets to the switch with the blocked port. When these test data packets are absent, the switch with the blocked port changes over the hitherto blocked port to a forwarding state. The ring portion has no redundancy manager provided for it in this case.
EP 1 575 221 A1 discloses a method for operating an Ethernet-based communication network that comprises a ring segment and a linear segment that is coupled to the linear segment at two coupling nodes. Both the ring segment and the linear segment have a respective dedicated redundancy manager provided for them. Furthermore, the two coupling nodes are in the form of a control network node and a corresponding partner network node and send one another test messages to detect interruptions in the linear segment. These test messages are intended not for the redundancy manager, however, but rather exclusively for the control network node and for the partner network node. Based on reception of these test messages, the control network node or the partner network node connects or disconnects a connection between the linear segment and the ring segment directly at the control network node or at the partner network node. The redundancy manager has dedicated test messages provided for it that are decoupled from the test messages interchanged between the control network node and the partner network node. The redundancy manager does not evaluate the test messages interchanged between the control network node and the partner network node.